Zinc oxide photoconductive element with an epoxy group containing interlayer

ABSTRACT

An electrophotographic copying material having a photoconductive layer formed on the surface of a support, whose back is precoated with an electroconductive layer, with an intermediary layer between said photoconductive layer and the support, said intermediary layer comprising a printing-durable polymer consisting of the reaction product of (A) a polymer having epoxy groups and (B) at least one member selected from the bridgemaking agent group consisting of water-soluble amino resin, amino compound, dibasic acid and acid anhydride.

United States Patent Arai et al. a

ZINC OXIDE PHOTOCONDUCTIVE ELEMENT WITH AN EPOXY GROUP CONTAINING INTERLAYER Inventors: Fumiaki Arai, Tokyo; Wasaburo Ohta; Junji Kurokawa, both of Yokohama; Noriyuki Usui, Kawasaki; Sakae Shimizu, Tokyo; Tetsuo Tanaka, Kasukabe, all of Japan Assignee: Kabushiki Kaisha Richo, Ota-ku,

Tokyo, Japan Filed: June 26, 1972 Appl. No.: 266,146

Related U.S. Application Data Continuation-impart of Ser. No. 830,252, June 4, 1969, Pat. No. 3,682,632.

U.S. Cl 96/1.8, 96/1.5, 101/462, 117/155 R, 117/155 UA, 117/161 LN, ll7/161UC,117/161ZB, 260/834, 260/835,

, 260/836 Int. Cl. G03g 5/04, 603g 5/08 Field of Search 96/1 R, 1.5, 1.6-1.8;

[56] References Cited UNITED STATES PATENTS 3,170,790 2/1965 Clark 96/1.5 3,198,850 8/1965 Levantin 117/161 ZB X 3,102,043 8/1963 Winthrop et al.......... 117/161 213 X FOREIGN PATENTS 0R APPLICATIONS 1,102,348 2/1968 Great Britain 96/1.8

Primary Examiner-R0land E. Martin, Jr. Attorney-Woodhams, Blanchard & Flynn [57] ABSTRACT An electrophotographic copying material having a photoconductive layer formed on the surface of a support, whose back is pre-coated with an electroconduc tive layer, with an intermediary layer between said photoconductive layer and the support, said intermediary layer comprising a printing-durable polymer consisting of the reaction product of (A) a polymer having epoxy groups and (B) at least one member selected from the bridge-making agent group consisting of water-soluble amino resin, amino compound, dibasic acid and acid anhydride.

2 Claims, N0 Drawings ZINC OXIDE PHOTOCONDUCTIVE ELEMENT WITH AN EPOXY GROUP CONTAINING INTERLAYER CROSS REFERENCE TO RELATED APPLICATION This application is a and continuation-in-part of our copending application Ser. No. 830 252, filed June 4, 1969 now US. Pat. No. 3,682,632, filed Aug. 8, 1972.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic copying material suitable for both the wetdeveloping process and the dry-developing process, which has a photoconductive layer formed on the surface of a support, whose back is precoated with an electroconductive layer, with an intermediary layer between said photoconductive layer and the support, said intermediary layer comprising a printing-durable polymer consisting of the reaction product of (A) a polymer having epoxy groups and (B) at least one member selected from the bridge-making agent group consisting of water'soluble amino resin, amino compound, dibasic acid and acid anhydride.

2. Description of the Prior Art The conventional electrophotographic copying material employed for an offset printing plate in the prior art has been prepared using a paper or fibrous support, one side of which has been previously processed for electroconductivity, and which is provided with an intermediary layer formed by coating the opposite side thereof with a resin solution such as polyvinyl alcohol, polyvinyl acetate, etc. The surface of the thus formed intermediary layer is further coated with a dispersion consisting of a photoconductive substance such as zinc oxide and the like, a resinous binder such as acrylic resin, alkyd resin and the like, and a sensitizer, thereby forming a photoconductive layer. In order to obtain an offset printing plate by employing a copying material as above, the surface of said photoconductive layer is first electrified with corona discharge, and then an original optical image is exposed onto the thus electrified surface to thereby form an electrostatic latent image, and subsequently a copied image is formed through either a dry-developing process or a wet-developing process, and lastly the non-image areas are made hydrophilic by means of a treating solution containing inorganic and organic ions.

During the foregoing copying process, the electric potential impressed on the photoconductive layer is required not to easily decay by virtue of conduction through the intermediary layer as well as the support. Such phenomenon of the potential decay, that is, the so-called dark decay is much influenced by the electric efficiency of the intermediary layer -such as electric insulating property, ion property, etc.as well as physical and chemical efficiency such as hydroscopicity and the like, while, at the time of exposure said electric potential is required to decay rapidly. The characteristic curve of said dark decay is desired to be almost constant under normal humidity or a high humidity and deterioration thereof under a high humidity should be as little as possible. Therefore, the back of the copying material is coated with an electroconductive substance such as polyvinylbenzyltrimethylammoniumchloride or other surfactant so as to facilitate the escape of electric charge therefrom. As to the process of making the copying material hydrophilic, inasmuch as a treating solution can easily permeate through the photoconductive layer up to the intermediary layer, said intermediary layer is required to have a sufficient water-resisting property as well as interlayeror wet-adhesive property. Should a photoconductive layer fail to meet these requirements, it will result in easy exfoliation in the course of offset printing. As to the manufacturing process of a copying material on the other hand, inasmuch as the surface of the intermediary layer is to be coated with a photoconductive-layerforming dispersion (which employs water or an organic solvent such as toluene, etc. as a dispersion medium), said intermediary layer is required to have an adequate solvent-resisting property and smoothness of the surface thereof (clay is ordinarily employed as a surfacesmoothing agent). Since the copying efficiency (viz. image formability) of a copying material provided with an intermediary layer and the printability of said material when employed for an offset printing plate need to meet such requirements as stated above, selection of a material suitable for said inter-layer is a matter of great importance.

However, none of the conventional electrophotographic copying materials has been provided with an intermediary layer capable of satisfying all of these re quirements. That is, for instance, a copying material employing such a resin as polyvinyl alcohol, polyvinyl acetate, etc. has been attended with defects in respect to water-resisting property, solvent-resisting property, adhesive property or printing endurance thereof and, consequently, has been inadequate as an offset printing plate for producing large numbers of printed copies. Therefore, varieties of proposals have so far been made with a view to remedying these defects. Typical proposals in this sphere include, for example, a copying mate rial having an adhesive layer sandwiched inbetween the intermediary layer and the photoconductive layer (J apanese Pat. No. Showa 40-7332) or a copying material provided with an intermediary layer consisting of a reaction product between a polymer having a reactive functional group such as a hydroxyl group, carboxyl group, etc. and an initial-stage condensate of amino resin (viz. amino-blast) such as trimethylol melamine and the like (Japanese Pat. No. Showa-40-l 8708). However, in case of the former of the above cited proposals, the printability is admittedly improved to some extent, but it requires provision of three layers, to wit, an intermediary layer, an adhesive layer and a photo conductive layer and, therefore, it is not only uneconomical but also apt to give rise to lack of uniformity of efficiency, while, in case of the latter, it has such a drawback that the residual formaldehyde within the intermediary layer is apt to volatilize to thereby decompose the sensitizer (viz. a dye) contained in the photoconductive layer or give rise to a change of quality of said photoconductive layer with the lapse of time to thereby cause deterioration of preservability as well as degeneration of the electrostatic properties and printability thereof.

SUMMARY OF THE INVENTION The present invention provides an electrophotographic copying material having an improved intermediary layer, with a view to elimination of the above stated shortcomings of the copying materials in the prior art and also the provision of a copying material having superb electrostatic properties as well as printing endurance suitable for the offset printing plate.

This composition comprises the reaction product of a polymer containing an epoxy group and at least one member of the bridge-making agent group consisting of a water-soluble amino resin, an amino compound, a dibasic acid and an acid anhydride.

Said polymer containing an epoxy group means a polymer comprising such monomers as glycidic acid or ester thereof, glycidyl methacrylic acid or ester thereof, etc., or other monomers having an epoxy group---for instance, a manufacture of Nippon Oil and Fats Co., Ltd. sold under the name Blenmer G (which is a vinyl monomer having an epoxy group)---and includes one or more of such compounds capable of copolymerizing with an epoxy group as styrene, acrylic acid or ester thereof, methacrylic acid or ester thereof, acrylonitrile, vinyl chloride, vinylidene chloride, vinyl acetate or ethylene. However, a polymer containing an epoxy group according to the present invention is not necessarily limited to one produced by the foregoing process of preparation.

As for the water-soluble amino resin, it is an initialstage condensate compound of amino resin such as melamine-formaldehyde resin, urea-formaldehyde resin, etc. and it includes dimethylol melamine, trimethylol melamine, dimethyl-trimethylol melamine, urea-formaldehyde, etc. Said amino compound includes the group of amines such as ethylene diamine, diethylene triamine, diethylaminopropyl amine, mphenylene diamine, etc. or a polyamine such as a copolymer of acrylic amide and ethyl acrylate. Further, said dibasic acid includes, for example, oxalic acid, succinic acid, etc., and the acid anhydride includes the anhydrides of dicarboxylic acids such as phthalic anhydride, succinic anhydride, etc. Any of these substances may be employed as a bridge-making agent. The weight ratio is in the range of 0.00l0.2 part by weight of said bridge-making agent per 1 part by weight of the aforesaid polymer having epoxy group.

The above-mentioned polymer containing an epoxy group which comprises the major proportion of the intermediary layer, is prepared, for instance, by heating and polymerizing methyl methacrylate and glycidyl methacrylate in the presence of a radical catalyzer such as ammonium persulfate, a nonionic-type emulsifier such as sodium lauryl benzenesulfonate, sodium dodecyl benzenesulfonate, etc., and a stabilizer such as polyvinyl alcohol. The thus obtained reactive polymer containing an epoxy group is employed, together with the above mentioned bridge-making agent such as an initial-stage condensate of amino resin, an amino compound, etc., as well as a catalyzer and, if necessary, an electroconductive agent, for preparing a dispersion. The resultant dispersion is then coated on the surface of a support and is dried to thereby form an intermediary layer on said support. The thus formed intermediary layer is therefore presumably provided with complex network structures by virtue of the bridging between the foregoing materials.

Subsequently, by means of coating a photoconductive-layer-forming dispersion comprising such well-known materials as zinc oxide, resinous binder, sensitizer and so on the surface of an intermediary layer provided as above, a photoconductive layer is formed and an electrophotographic copying material is obtained. In case where any such a support as has not been processed for electroconductivity is to be employed, it will suffice to coat one side of said support with a electroconductive-layer-formable dispersion comprising the above-stated intermediary-layerforming dispersion, an electroconductive agent and, if necessary, a surface-smoothing agent, to thereby form an electroconductive layer on the support.

Inasmuch as the electrophotographic copying material thus obtained according to the present invention is provided with an intermediary layer having network structures as stated above, it is characterized by the fact that not only are its water-resisting qualities, solvent-resisting qualities and durability much improved, but also its dark-decay properties are by no means affected, and, as a result a clear-cut copied image can be obtained therefrom. Furthermore, it demonstrates a superb durability when employed for an offset printing plate so that a stable mass-printing can be effected thereby.

DSCRIPTION OF THE PREFERRED EMBODIMENTS This invention will be further described with reference to the following illustrative Examples.

EXAMPLE 1 A mixture (c) comprising: methyl methacrylate parts by weight butyl laurate 30 parts by weight glycidyl methacrylate 15 parts by weight ammonium persulfate 0.25 parts by weight sodium laurylbenzene sulfonate 1.1 parts by weight hydroxyethyl cellulose 0.5 parts by weight water 120 parts by weight was caused to react for 6 hours at C, whereby an epoxy resin was prepared. A dispersion was then prepared by dispersing parts by weight of said epoxy resin, 10 parts by weight of dimethylol melamine and 3 parts by weight of ammonium chloride in 100 parts by weight of water, and was coated on one side of a slick paper (pulp ratio of N/L: 50/50, thickness: 65p.) by means of an air-doctor and was dried for 1 minute at C, whereby an intermediary layer was formed on the surface of said paper support.

Subsequently, another dispersant was prepared by dispersing 100 parts by weight of said epoxy resin prepared by using the above mixture (c), 50 parts by weight of 20% aqueous solution of polyvinyl alcohol, 15 parts by weight of dimethylol melamine, 3 parts by weight of ammonium chloride, 100 parts by weight of clay, 0.3 part by weight of sodium hexametaphosphate and 20 parts by weight of polyvinylbenzyltrimethylammonium chloride in 500 parts by weight of water, and was coated on the non-coated side of said paper support in the same way as in case of forming the foregoing intermediary layer and was dried for l minute at 150C, whereby an electrconductive layer was formed on the back of said support.

The amount of resin contained in the coating-layers was 7g/m for the intermediary layer and IOg/m for the electroconductive layer, respectively, and the surfaces of both layers, having no pinhole or flaw thereon, were quite smooth, and the resultant support was covered with a perfect resin film. Further, in case where the intermediary layer side of the support was immersed for 1 hour in toluene which is employed in the subsequent photoconductive-layer-forming process, but there was observed no change at all.

Next, a photoconductive-layer-forming acrylic resin was prepared by causing a mixture comprising 45 parts by weight of styrene, 22 parts by weight of butyl acrylate, 30 parts by weight of methyl methacrylate, 3 parts by weight of acrylic acid and 100 parts by weight of toluene to react for hours at 100C. Then, a dispersion prepared by dispersing 40 parts by weight of said acrylic resin, 100 parts by weight of zinc oxide and Ice each of 0.25%-methanol solution of Rose Bengal and 1% methanol solution of Bromophenol Blue in 150 parts by weight of toluene was coated on the surface of the aforesaid intermediary layer of the support and was dried for 1 minute at 130C, whereby an electrophotographic copying material provided with a photoconductive layer of 10p thick was prepared.

The electrophotographic copying material thus obtained proved to have superb preservability, durability and water-resisting property as well as satisfactory adhesive property to bind the intermediary layer and the photoconductive layer thereof. Besides, the dark decay of the photoconductive layer thereof was quite slight, showing a remarkable improvement as compared with conventional copying materials. Further, the copied image obtained through dry development as well as wet development of a copy duplicated by this copying material retained a continuous gradation of high fidelity, and there was observed no influence on the developer due to the intermediary layer or the electroconductive layer thereof.

EXAMPLE 2 A mixture (d) comprising:

methyl methacrylate 50 parts by weight ethyl acrylate 50 parts by weight glycidyl methacrylate parts by weight ammonium persulfate 0.25 parts by weight sodium laurylbenzene sulfonate 1.1 parts by weight polyvinyl alcohol 0.5 parts by weight water 120 parts by weight was caused to react for 6 hours at a temperature in the range of 75- 80C, whereby an epoxy resin was synthesized. Then, a dispersant prepared by dispersing 100 parts by weight of said epoxy resin, 3.0 parts by weight of trimethylol melamine, parts by weight of thermoplastic acrylic resin emulsion and 3 parts by weight of ammonium chloride in 120 parts by weight of water was coated on one side of a slick paper (pulp ratio of NI]. 50/50, thickness: 95p.) in the same way as in the case of forming the intermediary layer of Example 1 and was dried, whereby an intermediary layer was formed on the back of said paper support.

Subsequently, another dispersion was prepared by dispersing 100 parts by weight of said epoxy resin obtained by using the above mixture (d), 50 parts by weight of 20% aqueous solution of polyvinyl alcohol, 15 parts by weight of trimethylol melamine, 3 parts by weight of ammonium chloride, 100 parts by weight of clay, 0.3 part by weight of sodium hexametaphosphate and 20 parts by weight of polyvinylbenzyltrimethylammonium chloride in 500 parts by weight of water, and was coated on the non-coated side of said paper support in the same way as in case of forming the foregoing intermediary layer, whereby an electroconductive layer was formed on the back of said support.

The amount of resin contained in the foregoing intermediary layer and electroconductive layer was 6.5g/m and 9g/m respectively, and the surface of said intermediary layer was stable against toluene and displayed a satisfactory water-resisting property.

Next, a photoconductive layer of the same composition as Example 1 was formed in the same way as in said example on the surface of said intermediary layer, whereby an electrophotographic copying material was obtained. In this case, said photoconductive layer was 12p. thick.

The electrophotographic copying material thus obtained demonstrated preservability, durability and water-resisting property equivalent to that of the preceding Example, and even in case where it was employed for an offset-printing plate, it was stable against etching liquid or immersion water and any deformation or damage was not observed even after producing more than 4,000 prints. Further, as for the copied image, it could reproduce an image quite faithful to the original.

EXAMPLE 3 A mixture (e) comprising:

butyl acrylate 50 parts by weight styrene 50 parts by weight glycidyl methacrylate 15 parts by weight ammonium persulfate 0.25 parts by weight sodium laurylbenzene sulfonate 1.1 parts by weight polyvinyl alcohol 0.5 parts by weight water 120 parts by weight was caused to react for 6 hours at a temperature in the range of C, whereby an epoxy resin was synthesized.. Then, a dispersion prepared by dispersing parts by weight of said epoxy resin, 7 parts by weight of urea-formaldehyde resin and 3 parts by weight of ammonium chloride in 100 parts by weight of water was coated on one side of a slick paper (pulp ratio of N/L 50/50, thickness: 60p.) in the same way as in case of forming the intermediary layer of Example 1, whereby there was formed an intermediary layer on the surface of said paper support.

Subsequently, another dispersion was prepared by dispersing 100 parts by weight of said epoxy resin obtained by using the above mixture (e), 50 parts by weight of 20% -aqueous solution of polyvinyl alcohol, 30 parts by weight of dimethylol melamine, 3 parts by weight of ammonium chloride, 100 parts by weight of clay, 0.3 part by weight of sodium. hexametaphosphate and 20 parts by weight of polyvinylbenzyl-trimethylammonium chloride in 500 parts by weight of water, and was coated on the non-coated side of said paper support according to the method of forming the electroconductive layer of Example 1, whereby an electroconductive layer was formed on the back of said support.

The amount of resin contained in the intermediary layer was 6g/m and Sg/m, respectively, and the surface of said intermediary layer demonstrated a superb water-resisting property.

Next, a photoconductive layer consisting of 100 parts by weight of zinc oxide, 40 parts by weight of vinyl acetate-crotonic acid copolymer (a manufacture of Japan Synthetic Chemical Co., Ltd. sold under the name GOSERAN), 2cc of 28% ammonia water, 1.5cc each of 0.5% methanol solution of erythrosine, 0.5% methanol solution of fluorescene and 1% methanol solution of Bromophenol Blue as a sensitizer and 10000 of water was coated on the surface of said intermediary layer and was dried for 3 minutes at 160C, whereby an electrophotographic copying material with a photoconductive layer of p. thick formed on the surface of said intermediary layer was obtained.

The photoconductive layer of the thus prepared electrophotographic copying material, when compared with. the photoconductive layer of an electrophotographic copying material having an intermediary layer consisting mainly of conventional polyvinyl alcohol, proved to have been improved by 50% or more with respect to the dark decay characteristics thereof. Besides, the copied image produced thereby was satisfactory, having a high concentration of image.

EXAMPLE 4 An intermediary-layer-forming aqueous dispersion consisting of 100 parts by weight of the epoxy resin synthesized by using the mixture (c) in Example 1, 10 parts by weight of ethylenediamine, 3 parts by weight of ammonium chloride and 100 parts by weight of water and a photoconductive-layer-forming aqueous dispersion consisting of 100 parts by weight of the foregoing epoxy resin, 50 parts by weight of polyvinyl alcohol, 30 parts by weight of ethylene diamine, 3 parts by weight of ammonium chloride, 100 parts by weight of clay, 0.3 part by weight of sodium hexametaphosphate, 30 parts by weight of polyvinylbenzyltrimethylammonium chloride and 500 parts by weight of water were respectively coated on one side of the same slick paper support as that of Example 16 and dried, whereby an intermediary layer and an electroconductive layer were formed on the surfaces and the back of said support respectively.

The amount of resin contained in the thus formed intermediary layer and electroconductive layer was 7.5g/m and 9g/m respectively. The surface of said intermediary layer did not show any change even when immersed in toluene.

Subsequently, a photoconductive-layer-forming toluene dispersion having the same composition as the photoconductive layer of Example 1 was coated on the surface of the foregoing intermediate layer to form a photoconductive layer thereon, whereby an electrophotographic copying material was prepared. The thus obtained electrophotographic copying material proved satisfactory in durability as well as water-resisting property thereof, and was provided with a mighty adhesive property to bind said photoconductive layer and intermediary layer, so that even after a long-term preservation, there was observed no change in its quality. Besides, the dark decay characteristic of its photoconductive layer proved to have been remarkably improved and the occurrence of such phenomena as curling and so on decreased.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In an electrophotographic copying material comprised of an electroconductive paper support, an intermediate layer and a photoconductive layer containing photoconductive zinc oxide, the improvement wherein said intermediate layer consists essentially of the reaction product of (A) a polymer having epoxy groups obtained by polymerizing glycidic acid or ester thereof, or

glycidyl methacrylate or a vinyl monomer having an epoxy group, with styrene, acrylic acid or ester thereof, methacrylic acid or ester thereof, acrylonitrile, vinyl chloride, vinylidene chloride, vinylacetate or ethylene, and (B) at least one bridge-making agent selected from the group consisting of a. water-soluble amino resin selected from the group consisting of dimethylol melamine, trimethylol melamine, dimethyl-trimethylol melamine and urea-formaldehyde,

b. amino compound selected from the group consisting of ethylene diamine, diethylene triamine, diethylamino-propylamine, m-phenylene diamine and copolymer of acrylic amide and ethyl acrylate,

c. dibasic acid selected from the group consisting of oxalic acid and succinic acid and d. acid anhydride selected from the group consisting of phthalic anhydride and succinic anhydride.

2. An electrophotographic copying material as claimed in claim 1, in which said intermediate layer contains from 0.001 to 0.2 parts by weight of bridgemaking agent per one part by weight of said polymer.

UNITED STATES .PATEM OFFICE CERTIFICATE OF CORRECTION Patent No. 3 778 264 Dated December 11, 1.973

Fumiaki Arai, Wasaburo Ohta; Junji Kurokawa, Inventor(s) Noriyuki Usui Sakae Shimizn and Tetsuo 'Ianaka It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the Heading, please insert the following:

we Foreign Application Priority Data June 14, 1968 Japan 40585/68 sept. 9, 1968 Ja an 64277/68 Oct. 1 2, 1 968 Japan 71153/68 Oct. 9, 1963 Japan 73174 68 I 0e11, 12, 1968 Ja n 74449/68 Change the Spelling of the Assignee's name to the following:

er-Assigneez Kabushiki Kaisha Ric'oh Signed and sealedthis 16th day of July 197 (SEAL) Attest: p

' MCCOY M. GIBSON, JR. C. MARSHALL DANN Attesting Officer Commissioner of Patents F ORM P04 050 (10-69) USCOMM-DC 603764 69 U. 5. GOVERNMENT PRINTING O FFICE I969 O3$6-33l. 

2. An electrophotographic copying material as claimed in claim 1, in which said intermediate layer contains from 0.001 to 0.2 parts by weight of bridge-making agent per one part by weight of said polymer. 